π-Extension of a 4-ethoxy-1,3-thiazole via aryl alkyne cross coupling: synthesis and exploration of the electronic structure

Abstract

A series of four donor aryl alkynyl substituted thiazole derivatives 3a-d and three similar aryl donor-acceptor systems 6a-c have been synthesized. All compounds bear different electron-donating groups in the 5-position of the thiazole core. The influence of both electron donor strength and the additional phenylethynyl unit on photophysical properties, i.e. UV/Vis absorption, fluorescence emission and fluorescence lifetime, has been evaluated. Additionally, theoretical calculations have been performed at the CAM-B3LYP/6-31+G(d,p) level and good agreement with the experimental data has been achieved. The new derivatives synthesized via palladium catalyzed cross coupling are characterised by moderately strong emission between 474 and 538 nm (ΦF = 0.35-0.39) and Stokes' shifts ranging from 0.54 to 0.79 eV (4392-6351 cm(-1)). The smaller chromophores of type 6 exhibit modest to high fluorescence emission (ΦF = 0.45-0.76) between 470 and 529 nm and their Stokes' shifts range from 0.59 to 0.65 eV (4765-5251 cm(-1)).

Assembly of T-Shaped Amphiphilic Thiazoles on the Air–Water Interface: Impact of Polar Chromophore Moieties, as Well as Dipolarity and π-Extension of the Chromophore on the Supramolecular Structure

“…Finally, Am and Py show similar monomeric absorption and emission features and the same dependencies on molecular substitutions, namely, the Me , Br , Bi , and BiSulf substituents causing red shifts of the absorption and emission spectra with successive π-system extension ( Bi always yielding the largest red shift). These results are in good agreement with the literature. − , Whereas the Am and Py derivatives easily dissolve in the broad range of different polar solvents (except their BiSulf derivatives), the Ni derivatives show fluorescence peaks assigned to aggregates, even in the dilute solutions. Because of their spectral shifts as compared to the monomers, we deduce dipolar aggregation in the case of the Ni derivatives, which is expected to impact supramolecular structure formation at the air–water interface as discussed next.…”

“…However, all spectra of the Py derivatives are blue-shifted as compared to their Am counterparts (compare Figure with Figure ; see Table ), which is in agreement with reports on similar chromophores . This difference in the spectral position increases with shortening of the π-system, that is, as most pronounced for the ( Am / Py ) Me derivatives.…”

“…A further expansion of the chromophore is possible by cross-coupling of the 5-(4-bromophenyl) substituent. Several different cross-coupling reactions, like Buchwald–Hartwig aminations, , Sonogashira cross-coupling, or Stille cross-couplings, have already been described for 5-bromophenyl thiazoles. Still, no Suzuki reactions on these dyes are known to date.…”

“…A further expansion of the chromophore is possible by cross-coupling of the 5-(4bromophenyl) substituent. Several different cross-coupling reactions, like Buchwald−Hartwig aminations, 58,62 Sonogashira cross-coupling, 63 or Stille cross-couplings, have already been With the successful syntheses of 4, 8, and 9, the ester group of the hexanoate side chain needs to be saponificated to yield the amphiphilic anchor group. Recently, the deprotection of such alkyl esters of 4-alkyoxy thiazoles was published using an anhydrous ethanolic potassium hydroxide solution.…”

Mixing Chromophores: Donor–Acceptor Dyes with Low‐Lying LUMOs and Narrow Band Gaps by Connecting 4‐Alkoxythiazoles and Azaacenes

“…Indeed, the phenothiazine donor bearing systems PyrS and BtS show the most redshifted emission within their class of acceptors, but also the weakest emission, which could be assigned to the additional sulfur atom. Sulfur is known for promoting intersystem crossing through spin‐orbit coupling, which contributes energetic deactivation …”